The present invention relates generally to wrapped hard disk drives and methods for improved sealing thereof using metallic material.
Coating surfaces on hard disk drives is known for a variety of purposes. One such purpose is for containment of a gaseous medium within the hard disk drive. U.S. Patent Publication No. 2012/0275105 A1 describes providing at least one metal coating over at least a portion of an exterior surface of a hard disk drive. Coating a hard disk drive as such is described as providing improved sealing of inert gases within a hard disk drive. While effective for sealing inert gases within a hard disk drive, such methods typically require specialized processing equipment and methodology for application of the metal coating. For example, formation of a metal coating using sputter coating methodology requires use of costly sputter chambers for coating of the hard disk drive and tightly controlled processing conditions during manufacture of such hard disk drives.
Materials other than metal are also coated on hard disk drives for sealing and additional purposes. For example, U.S. Patent Publication No. 2012/0275286 A1 describes encapsulation of hard disk drives with polymeric coatings. The polymeric coatings are described as providing protective and/or decorative properties to the hard disk drive. U.S. Pat. No. 5,454,157 describes a disk drive assembly containing a metallic base and cover. In order to minimize escape of helium or nitrogen contained therein (via porosity in the metallic base and cover plates), a special electrostatic coating process and material called “E-coat” are used. E-coating, which is said to be a commercially available coating material and is known to be an insulative epoxy material, is applied to the surfaces of the base and cover as well as all other surfaces making up the hermetically sealed chamber. Such application of the E-coating takes place before the plates are assembled together. Every surface, inner and outer, of each plate is completely coated with a black E-coating as such. With the E-coating applied, the overall sealed chamber's porosity is purportedly lowered ninety-seven percent to an acceptable amount in order to contain the helium and nitrogen gas.
A hermetic seal is generally understood to be an airtight seal. Note that some seals (e.g., those “sealing” air within the hard disk drive) are not literally air tight, but rather utilize an extremely fine air filter in conjunction with air circulation inside the hard drive enclosure. The spinning of the disks causes air to circulate therein, forcing any particulates to become trapped on the filter. The same air currents also act as a gas bearing, which enables the heads to float on a cushion of air above the surfaces of the disks. However, “hermetically” sealed means that the seal is so airtight that the disk drive's internal pressure is substantially independent of the external or ambient pressure. This is in contrast to a conventional or non-hermetically sealed disk drive that has a breather port with a filter in a wall of the base plate or cover for equalizing the disk drive's internal pressure with the external pressure. Thus, a hermetically sealed drive does not contain a breather port.
Within a hermetically sealed hard disk drive, gases other than atmospheric air are often employed. Filling the sealed environment of a hard disk drive with gases other than air can enhance their performance. For example, use of lower density inert gases, such as helium, can reduce aerodynamic drag between the disks and their associated read/write heads by a factor of approximately five-to-one as compared to their operation in air. This reduced drag beneficially results in reduced power requirements for the spindle motor. A helium-filled drive, thus, uses substantially less power than a comparable hard disk drive operating in an air environment. At the same time, the helium gas also conducts heat generated during operation of the disk drive away more effectively than air.
Hermetically sealed hard disk drives are first filled with a desired gaseous medium (whether it be atmospheric air or one or more other gases) before operation. Then, if the constituency of the gaseous medium substantially changes due to leakage of the hard disk drive housing, the hard disk drive must be either discarded or refilled with the desired gaseous medium. Filling disk drives to a desired pressure and concentration of gaseous components, however, can be both time-consuming and difficult. A number of patent documents focus on providing and/or replenishing gases such as helium at a desired concentration within a hard disk drive. See, for example, U.S. Patent Publication Nos. 2003/0081349 and 2003/0089417. Also see U.S. Pat. No. 6,560,064.
Due to imperfect sealing of hard disk drive housings, the benefits of using lower density gases such as helium are conventionally not longstanding. Potential paths of leakage (allowing both air flow into the hard disk drive housing and allowing gas outflow from the hard disk drive housing) include those paths existing at the junction of two mating components thereof. Those components include, for example, screws or other mechanical fasteners used to conventionally fasten multiple parts of the housing together. In addition, gasket seals and the like used to improve the seal between multiple components are often susceptible to at least some leakage. As gas such as helium leaks out of a sealed hard disk drive, air leaks in (or vice versa), causing undesirable effects in the operation of the disk drives—even possibly causing the disk drives to catastrophically fail. For example, an increased concentration of air inside the hard disk drive may increase forces on the read/write head therein due to turbulent airflow within the drive. Further, such undesired air may cause the read/write heads to “fly” at too great a distance above the disks. The risk of unexpected failure due to inadequate concentration of helium within such drives is a considerable drawback to helium-filled disk drives, particularly since the data stored within the disk drive can be irretrievably lost if the disk drive fails.
Conventional problems associated with helium-filled hard disk drives are being overcome, but solutions are slow to evolve. Recently, HGST, a Western Digital company, announced its 6 TB Ultrastar He6 hard disk drive based on HGST's trademarked HelioSeal technology. According to a 2013 press release, such technology provides the industry's first helium-filled platform that simultaneously increases disk drive capacity while lowering its power consumption and operating temperature.
Effective cooling of hard disk drives is becoming a notable challenge due to increased power consumption and associated generation of heat in high performance devices, but with less space for efficient airflow as device sizes decrease. One solution for decreasing hard disk drive operating temperature that has been explored is liquid cooling. Liquid, which is denser than air, can remove heat more efficiently and maintain a more constant operating temperature. While traditional hard disk drives cannot be submerged as they are open to the atmosphere and would allow the cooling liquid inside, damaging or destroying the hard disk drive, HGST's HelioSeal™ platform is also described by HGST as providing a cost-effective solution for liquid cooling as the drives are hermetically sealed and are described as enabling operation in most any non-conductive liquid.
Thus, sealing of hard disk drives is desired for not only containment of a gaseous medium within the hard disk drive, but for prevention of entry of liquid medium external to the hard disk drive. With a growing emphasis on increasing storage density and decreasing device size, reduction of power consumption and reduction of heat generated during operation of hard disk drives is increasingly important.
Overheating is purported to be a common cause of hard disk drive failure. Overheating can, for example, cause platters in the drive to expand. If the disk's read-and-write head comes in contact with the disk's surface, a catastrophic head crash can result. Immersion of certain hard disk drives in liquid cooling mediums is, thus, being explored. For example, 3M Co. (St. Paul, Minn.) markets engineered fluid heat transfer medium under the NOVEC trade designation for use with electronic components. In order to take advantage of such liquid cooling mediums, effective sealing of a hard disk drive to eliminate or minimize leakage is desired.
Elimination of or minimization of leakage is desired for other reasons as well. One such reason relates to a reduction of complications arising from electromagnetic interference. Electromagnetic interference (“EMI,” also called radio frequency interference or “RFI”) is a usually undesirable disturbance caused in an electrical circuit by electromagnetic radiation emitted from an external source. Such disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit.
EMI can be induced intentionally for radio jamming, as in some forms of electronic warfare, or unintentionally, as a result of spurious emissions and responses, intermodulation products, and the like. A source of EMI may be any object, artificial or natural, that carries rapidly changing electrical currents, such as another electrical circuit or even the sun or Northern Lights. Broadcast transmitters, two-way radio transmitters, paging transmitters, and cable television are also potential sources of EMI within residential and commercial environments. Other potential sources of EMI include a wide variety of common household devices, such as doorbell transformers, toaster ovens, electric blankets, ultrasonic pest controls (e.g., bug zappers), heating pads, and touch-controlled lamps. It is known that EMI frequently affects the reception of AM radio in urban areas. It can also affect cell phone, FM radio, and television reception, although to a lesser extent. EMI can similarly affect performance of a computer.
In conventional disk drives, unwanted and potentially problematic EMI wavelengths can enter a disk drive through a number of places. For example, similar to paths of gas leakage, such wavelengths can enter disk drive housings around screws used to hold multiple components of the housing together. Junctions where components of the hard disk drive housing (e.g., cover and base) meet are another potential path of gas leakage.
Within integrated circuits, the most important means of reducing EMI include the following: the use of bypass or “decoupling” capacitors on each active device (connected across the power supply and as close to the device as possible), risetime control of high-speed signals using series resistors, and Vcc filtering. If all of these measures still leave too much EMI, shielding such as using radio frequency (RF) gasket seals (which are often very expensive) and copper tape has been employed. Another method of reducing EMI is via use of metal hard disk drive components. While the use of metal components undesirably increases the overall weight of an apparatus, use of metal components has been conventionally mandated in the hard disk drive industry due to the EMI sensitivity of mechanical spinning components therein. Without mechanical spinning components therein, however, manufacturers of flash drives have taken advantage of the benefits of, for example, a plastic case for enclosure of the drive. See, for example, U.S. Pat. No. 7,301,776, which describes how metal material used for top and bottom plates of the drives described therein can be replaced by plastic as there are fewer EMI issues associated with flash memory devices as compared to mechanical spinning hard disk drives.
Another source of potential hard disk drive failure stems from electrostatic discharge (ESD). ESD refers to a sudden and momentary electric current that flows between two objects at different electrical potentials. The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment. Ways to eliminate problematic ESD are in need of improvement as performance demands of hard disk drives increase.
While the aforementioned problems typically arise based on events and/or materials external to a disk drive, other problems may arise based on events and/or materials internal to a disk drive. That is, design of components within conventional disk drives can contribute to hard disk drive failure. For example, plastic components are susceptible to outgassing and components made from conductive materials are prone to shedding of particles, both of which can cause catastrophic disk failure.
In view of the number of potential problems impacting effective and long-term performance of hard disk drives, alternative methods and apparatus for improved hard disk drives are desired. Most desired are those methods and apparatus with improved efficiency and reliability over conventional attempts to provide the same.